Control of artificial lighting of a scene to reduce effects of motion in the scence on an image being acquired

ABSTRACT

Motion of an image of a scene being captured by a digital image acquisition device is detected and used to control parameters of illumination of the scene by a flash lamp that is typically built into the device. Parameters that may be controlled include the intensity, duration and timing of light emitted by the flash lamp. Such control of the flash illumination is preferably performed in conjunction with adjusting one or more exposure parameters used to capture an image. Such exposure parameters include duration, aperture and sensor gain. Motion blur caused by movement of the camera or by movement of an object within the scene being photographed is reduced by selecting appropriate exposure parameters and flash light characteristics.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/709,667 filed on Feb. 22, 2010, which is a continuation of U.S.application Ser. No. 11/552,717 filed on Oct. 25, 2006, which are bothincorporated herein in their entirety by this reference.

BACKGROUND AND SUMMARY

This application relates to automatic exposure control of digitalcameras and other electronic digital image acquisition devices, andparticularly to the control of scene illumination by flash light duringthe capture of image data of the scene.

Electronic cameras image scenes onto a two-dimensional sensor such as acharge-coupled-device (CCD), a complementary metal-on-silicon (CMOS)device or other type of light sensor. These devices include a largenumber of photo-detectors (typically two, three, four or more million)arranged across a small two dimensional surface that individuallygenerate a signal proportional to the intensity of light or otheroptical radiation (including infrared and ultra-violet regions of thespectrum adjacent the visible light wavelengths) striking the element.These elements, forming pixels of an image, are typically scanned in araster pattern to generate a serial stream of data representative of theintensity of radiation striking one sensor element after another as theyare scanned. Color data are most commonly obtained by usingphoto-detectors that are sensitive to each of distinct color components(such as red, green and blue), alternately distributed across thesensor.

A popular form of such an electronic camera is a small hand-held digitalcamera that records data of a large number of picture frames either asstill photograph “snapshots” or as sequences of frames forming a movingpicture. A significant amount of image processing is typically performedon the data of each frame within the camera before storing on aremovable non-volatile memory such as a magnetic tape cartridge, a flashmemory card, a recordable optical disc or a removable hard disk drive.The processed data are typically displayed as a reduced resolution imageon a liquid crystal display (LCD) device on the outside of the camera.The processed data are also typically compressed before storage in thenon-volatile memory in order to reduce the amount of storage capacitythat is taken by the data for each picture frame.

The data acquired by the image sensor are typically processed tocompensate for imperfections of the camera and to generally improve thequality of the image obtainable from the data. The correction for anydefective pixel photodetector elements of the sensor is one processingfunction. Another is white balance correction wherein the relativemagnitudes of different pixels of the primary colors are set torepresent white. This processing also includes de-mosaicing theindividual pixel data to superimpose data from spatially separatemonochromatic pixel detectors of the sensor to render superimposedmulti-colored pixels in the image data. This de-mosaicing then makes itdesirable to process the data to enhance and smooth edges of the image.Compensation of the image data for noise and variations of the cameraoptical system across the image and for variations among the sensorphotodetectors is also typically performed within the camera. Otherprocessing typically includes one or more of gamma correction, contraststretching, chrominance filtering and the like.

Electronic cameras also nearly always include an automatic exposurecontrol capability that sets the exposure time, size of its apertureopening and analog electronic gain of the sensor to result in theluminescence of the image or succession of images being at a certainlevel based upon calibrations for the sensor being used and userpreferences. These exposure parameters are calculated in advance of thepicture being taken, and then used to control the camera duringacquisition of the image data. For a scene with a particular level ofillumination, a decrease in the exposure time is made up by increasingthe size of the aperture or the gain of the sensor, or both, in order toobtain the data within a certain luminescence range. An increasedaperture results in an image with a reduced depth of field and increasedoptical blur, and increasing the gain causes the noise within the imageto increase. Conversely, when the exposure time can be increased, suchas when the scene is brightly lighted, the aperture and/or gain arereduced, which results in the image having a greater depth of fieldand/or reduced noise. In addition to analog gain being adjusted, or inplace of it, the digital gain of an image is often adjusted after thedata have been captured.

It is often difficult for the user to hold a camera by hand during anexposure without imparting some degree of shake or jitter, particularlywhen the camera is very small and light. As a result, the captured imagemay have a degree of overall motion blur that depends on the exposuretime, the longer the time the more motion blur in the image. Inaddition, long exposures of a scene that is totally or partially movingcan also result in motion blur in the captured image. A person or objectmoving across the scene, for example, may appear blurred in the image.The automatic exposure processing of existing cameras does not take intoaccount motion of the camera or motion within the scene when calculatingthe exposure parameters to be used to capture an image of the scene.

U.S. patent application Ser. No. 11/258,975, filed Oct. 25, 2005,entitled “Camera Exposure Optimization Techniques That Take Camera andScene Motion into Account,” does consider image motion when settingexposure parameters. Motion is detected and the exposure parameters areset, in advance of capturing data of the image, to levels that enhancethe captured image based on the amount of motion of the scene relativeto the image frame within the camera. Blur of the image caused by eithercamera shake or local motion within the scene, or both, can be minimizedor even prevented by adjusting the exposure parameters. Conversely, incases where little or no motion is detected prior to capturing the imagedata, the exposure parameters may be set to optimize other aspects ofthe image, such as increasing the exposure time in order to allow thedepth of field to be increased and/or the level of noise to be reduced.

Motion is preferably measured by calculating motion quantities from dataof two or more images prior to capturing data of the final image (using“pre-capture” images). Motion quantities that define the amount ofmotion of the scene image relative to the camera, including motionwithin the scene, are preferably calculated. Such relative motionquantities may include direction, thereby being motion vectors, or mayjust express the magnitude of the motion. By this technique, localmotion vectors are individually calculated for distinct blocks of pixelswithin the image, which then allows motion within the scene to be takeninto account when calculating the exposure parameters. Global motionvectors, such as caused by camera shake, can also be calculated fromdata of the two or more pre-capture images. Although the presence ofmotion blur can be detected from data of a single image, the calculationof motion vectors from two or more pre-capture images is more preciseand leads to better control of the exposure parameters used tosubsequently capture the image. Use of a mechanical motion sensor, whichis included in some cameras, can only provide an indication of anyglobal motion, not individual motion of objects or portions within thescene being photographed.

The results of the image motion calculations may also be used toestimate future motion so that a time to capture data of the image maybe chosen where the absolute velocity of motion is at least less than atother times and possibly minimal. Particularly in the case of camerashake, where the motion often has some periodicity to it that can beforecasted, the picture can be taken at a time when the global motion iszero or near zero. The velocity of a portion of the scene can also beforecasted in the same way and a time chosen to take the picture whenthe local motion blur is minimized. When doing this forecasting, theexposure parameters are preferably calculated from the motion quantitiesthat are expected to exist at the time scheduled for capturing theimage.

In a specific implementation, when the ambient light is sufficient,preliminary exposure parameters are first calculated in the same manneras in existing cameras, without regard to any motion of the camera orportions of the scene image. If these preliminary parameters are atlevels where their adjustment is not likely to improve the quality ofthe image, then the image is captured with them and the results ofmotion calculations are not used. An example where this can occur iswith a brightly lighted scene, where the preliminary exposure time isnearly as short, the aperture nearly as small and the gain nearly as lowas the camera allows. In such a case, the exposure time can neither besignificantly shortened to limit any motion blur nor increased tosignificantly improve depth of field or reduce noise since the apertureand gain level are nearly as small as possible. But when this is not thecase, the preliminary exposure parameters are adjusted on the basis ofthe image motion calculations to reduce the amount of or eliminatemotion blur in the captured image.

According to improvements described herein, motion blur in the image mayalso be reduced or eliminated by controlling parameters of artificiallight illuminating the captured scene. This is done both when a lowlight level of a portion or the entire scene makes it desirable toilluminate the scene with artificial light, or when the ambientillumination is sufficient but use of artificial illumination improvesthe quality of the captured image. In a specific implementation, motionblur of the resulting image may be reduced or eliminated by controllingparameters of the artificial light instead of adjusting the exposureparameters for this purpose. Such light is typically provided by one ormore flash light sources, preferably built directly into the camera. Anyor all of the intensity, duration, number and timing of flash lightpulse(s) occurring during exposure may be controlled to reduce motionblur.

In yet another specific implementation, calculations of both theexposure parameters and those of artificial light that illuminates thescene may be made from the detected motion and these parameters thenused to capture an image of the scene. The exposure and artificial lightparameters cooperate to reduce or eliminate motion blur. They may alsobe selected to enhance the image by providing a more even luminanceacross it.

Further, when there is little or no motion of the image, the exposureduration and other parameters may at times be chosen according to theimproved techniques herein to eliminate the need for artificialillumination or reduce its strength, thereby resulting in a capturedimage with better quality. But generally, the improved techniquesdescribed herein primarily allow acquiring images of scenes with lowlevels of ambient illumination that require artificial illumination.Parameters of the artificial illumination are calculated from quantitiesof motion detected in the image in order to reduce or eliminate motionblur.

The precise control of flash or other artificial light described hereinis preferred over an approach of employing a sensor with greatersensitivity, and using the blur reducing techniques described inaforementioned U.S. patent application Ser. No. 11/258,975, withoutartificial illumination of the scene. This stems from the fact thatincreasing sensor sensitivity is becoming more difficult and expensiveeach year as the number of megapixels incorporated into the averageimage sensor used in a digital camera annually increases for competitivereasons. When the number of light gathering elements in a sensorincreases, the size of each element is reduced, with a correspondingreduction in the sensitivity of each element, due to each element havinga smaller area, and thus intercepting a lower amount of radiant energy.

The improved techniques of controlling exposure and/or artificial lightparameters are also preferred over other ways that have been used orsuggested for minimizing or eliminating motion blur in the image. Anextremely short duration electronic strobe flash can be used toeffectively stop any image motion so long as the exposure duration islimited to substantially the duration of the light pulse. But this alsocauses the resulting image to look very unnatural, with a brightly litforeground and a very dark background. The control of exposure and/orflash parameters by detected image motion that are described hereinallow better control of image brightness. For example, if the imagemotion is not extreme, the flash pulse may be made to have a longerduration than the short probe and thus a lesser intensity, thereby toprovide better balance in image luminance between the largely flashilluminated foreground and ambient illuminated background.

Another approach made unnecessary by the improved techniques describedherein is the use of optical stabilization to compensate for hand jitterthat is provided on some cameras. In one line of cameras, vibrationreduction lenses are used. A measurement of camera motion causes theposition of the lens to be moved in a manner that moves the image in adirection and distance across the photosensor that is equal and oppositeto the direction of image movement caused by motion of the camera. Thisis a complicated electro-mechanical system and cannot compensate formotion of one object within a scene relative to other objects of thescene.

Various aspects, advantages, features and embodiments of the presentinvention are included in the following description of exemplaryexamples thereof, which description should be taken in conjunction withthe accompanying drawings.

All patents, patent applications, articles, other publications,documents and things referenced herein are hereby incorporated herein bythis reference in their entirety for all purposes. To the extent of anyinconsistency or conflict in the definition or use of terms between anyof the incorporated publications, documents or things and the presentapplication, those of the present application shall prevail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a camera or other video acquisition device in whichthe exposure control techniques of the present invention may beimplemented;

FIG. 2 is a block diagram of some of the functional components of thevideo signal processor of the device of FIG. 1;

FIG. 3 is a flow chart showing a process of calculating and usingexposure parameters that takes image motion into account;

FIG. 4 represents an image frame with exemplary camera and scene motionvectors added to individual blocks of pixels;

FIGS. 5A-5D represent amounts of motion of the image frame of FIG. 4, inan illustrative example;

FIGS. 6A-6C show an example of automatic camera exposure parameters as afunction of the luminance of the captured image;

FIG. 7 illustrates a specific example of adjustments of the automaticcamera exposure parameters for different levels of motion;

FIG. 8 is a flow chart showing a process of calculating and using flashlight parameters that takes image motion into account;

FIG. 9 is a flow chart showing a process of calculating and usingexposure and flash light parameters that take image motion into account;and

FIG. 10 is a flow chart showing another process of calculating and usingexposure and flash light parameters that take image motion into account.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Video data acquired by a digital camera are typically processed tocompensate for imperfections of the camera and to generally improve thequality of the image obtainable from the data. The correction for anydefective pixel photodetector elements of the sensor is one processingfunction that may be performed. Another is white balance correctionwherein the relative magnitudes of different pixels of the primarycolors are set to represent white. This processing may also includede-mosaicing the individual pixel data to superimpose data fromspatially separate monochromatic pixel detectors of the sensor to rendersuperimposed multi-colored pixels in the image data. This de-mosaicingthen makes it desirable to process the data to enhance and smooth edgesof the image. Compensation of the image data for noise and variations ofthe camera optical system across the image and for variations among thesensor photodetectors may also be performed. Other processing typicallyincludes one or more of gamma correction, contrast stretching,chrominance filtering and the like. The processed data are then usuallycompressed within the camera by use of a commercially availablealgorithm before storage in a non-volatile medium.

Image motion may also be taken into account in advance of taking thepicture in order to optimize parameters of any artificial lighting,either alone or in conjunction with optimizing parameters of theexposure, in order to enhance the resulting image based on the amount ofmotion present. The amount of camera jitter is preferably determined bycomparing data of two or more pre-capture images, typically having lowerresolution than the final acquired image, rather than using a gyroscopeor other mechanical camera motion detector, although such a motiondetector may alternatively be used. The pre-capture images may also beused to determine an amount of motion of objects within the scene beingphotographed with respect to other objects in the scene.

Global and/or local motion of an image are used to optimize the timing,duration and level (strength) of flash illumination of a scene beingcaptured. In addition, one or more, or even all, of the followingmeasurements may be used in this optimization, not only to reduce oreliminate blur but to also improve other aspects of the quality of thecaptured image, particularly to make it appear more naturallyilluminated:

-   -   (1) Global ambient illumination conditions;    -   (2) Local ambient illumination conditions;    -   (3) Background light level;    -   (4) Dynamic range (uniformity) of the ambient lighting across        the scene being captured;    -   (5) Distance of an object of interest within the scene from the        camera;    -   (6) Reflectivity of the object of interest; and    -   (7) Color of the object of interest.        Electronic Camera Example

In FIG. 1, an example of a camera in which the present invention may beimplemented is schematically shown, which may be a still camera or avideo camera. It includes a case 11, an imaging optical system 13, usercontrols and indicators 15 that generate and receive control signals 17,a video input-output receptacle 19 with internal electrical connections21, and a card slot 23, with internal electrical connections 25. Anon-volatile memory card 27 is removably inserted into the card slot 23.Data of images captured by the camera may be stored on the memory card27 or in an internal non-volatile memory (not shown). Image data mayalso be outputted to another video device through the receptacle 19. Thememory card 27 can be a commercially available semiconductor flashmemory, small removable rotating magnetic disk or other non-volatilememory to which video data can be written by the camera.

The optical system 13 can be a single lens, as shown, but will normallybe a set of lenses. An image 29 of a scene 31 is formed in visibleoptical radiation through an aperture 32 and a shutter 33 onto atwo-dimensional surface of an image sensor 35. A motive element 34 movesone or more elements of the optical system 13 to focus the image 29 onthe sensor 35. An electrical output 37 of the sensor carries an analogsignal resulting from scanning individual photo-detectors of the surfaceof the sensor 35 onto which the image 29 is projected. The sensor 35typically contains a large number of individual photo-detectors arrangedin a two-dimensional array of rows and columns to detect individualpixels of the image 29. Signals proportional to the intensity of lightstriking the individual photo-detectors are obtained in the output 37 intime sequence, typically by scanning them in a raster pattern, where therows of photo-detectors are scanned one at a time from left to right,beginning at the top row, to generate a frame of video data from whichthe image 29 may be reconstructed. The analog signal 37 is applied to ananalog-to-digital converter circuit chip 39 that generates digital datain circuits 41 of the image 29. Typically, the signal in circuits 41 isa sequence of individual words of digital data representing theintensity of light striking the individual photo-detectors of the sensor35.

The photo-detectors of the sensor 35 typically detect the intensity ofthe image pixel striking them in one of two or more individual colorcomponents. Early sensors detect only two separate colors of the image.Detection of three primary colors, such as red, green and blue (RGB)components, is common. Currently, image sensors that detect more thanthree color components are becoming available.

Processing of the video data in circuits 41 and control of the cameraoperation are provided, in this embodiment, by a single integratedcircuit chip 43 (which may also include the analog-to-digital converterinstead of using the separate circuit chip 39). These functions may beimplemented by several integrated circuit chips connected together but asingle chip is preferred. In addition to being connected with thecircuits 17, 21, 25 and 41, the circuit chip 43 is connected to controland status lines 45. The lines 45 are, in turn, connected with theaperture 32, shutter 33, focus actuator 34, sensor 29, analog-to-digitalconverter 39 and other components of the camera to provide synchronousoperation of them. Signals in the lines 45 from the processor 43 drivethe focus actuator 34 and set the size of the opening of the aperture32, as well as operate the shutter 33. The gain of the analog signalpath is also set by the processor 43 through the lines 45. This gaintypically takes place in the analog-to-digital converter which, in thecase of a CCD sensor, is part of the sensor, or in the case of a CMOSsensor, is part of a separate analog-to-digital converter as shown inFIG. 1.

A separate volatile random-access memory circuit chip 47 is alsoconnected to the processor chip 43 through lines 48 for temporary datastorage. Also, a separate non-volatile memory chip 49 is connected tothe processor chip 43 through lines 50 for storage of the processorprogram, calibration data and the like. The memory 49 may be flashmemory, which is re-programmable, or a memory that is programmable onlyonce, such as a masked programmable read-only-memory (PROM) or anelectrically programmable read-only-memory (EPROM). A usual clockcircuit 51 is provided within the camera for providing clock signals tothe circuit chips and other components. Rather than a separatecomponent, the clock circuit for the system may alternatively beincluded on the processor chip 43.

A source 53 of artificial illumination, such as a flash lamp or othersource of light pulses, is preferably built into the camera case 11. Thesource 53 operates in response to control signals from the processor 43through control lines 55. The source 53 is chosen to be a type thatemits light pulses whose intensity and/or duration are controllable, andpreferably both. Certain types of flash lamps currently used in cameras,such as xenon flash lamps, have a limited adjustability of pulseintensity and duration but other sources of light suitable for use incameras, such white light-emitting-diodes (LEDs), are more continuouslycontrollable. The processor 43 preferably controls the timing, intensityand duration of a light pulse output of the light source 53. Use of thiscontrol capability to minimize effects of camera and/or image motionwhen acquiring data of an image is described below.

Multiple illumination sources may alternatively be installed in thecamera, pointing in different directions for the purpose of moreuniformly illuminating an image filed over a wider field of view. All ofthe one or more light sources installed in a camera are preferablycontrolled by the processor 43. As a further alternative, one or morelight sources may be located outside of the camera case 11 but it iscertainly easier to control the effect of illumination source(s) thathave a fixed physical relationship with the camera optics.

A motion sensor 54 may also be included within the camera housing 11,its output connected to provide a signal to the processor 43 that isproportional to any motion of the camera relative to the scene thatoccurs during the capture of data of an image of the scene. Camerajitter often occurs during the taking of pictures with a hand heldcamera. The motion sensor 54 may be a gyroscope, accelerometer or someother mechanical device that provides an electrical output proportionalto the magnitude and direction of motion of the camera. Somecommercially available cameras include such a device. However, asdescribed hereinafter, it is preferred to measure camera motion fromdata of preview images acquired prior to taking the picture. This alsoallows characteristics of any motion within the scene, such as movementof a person or other object across the scene, to be determined. Amechanical sensor within the camera cannot provide this.

A general block diagram of the processor chip 43, including portionsthat calculate and estimate motion, is given in FIG. 2. A processor 57,which may be general purpose or dedicated to the tasks herein, performscalculations on the image data and controls operation of the camera, inresponse to firmware stored in the flash memory 49 (FIG. 1). Digitaldata of successive image frames are received over lines 41 by aninterface circuit 59 through input contacts on the chip 43, and are thencommunicated with other system components by connection through a memorymanagement unit 61. Video data of captured image frames are outputtedthrough an interface circuit 63 to lines 21 (to the input-outputreceptacle 19 of FIG. 1) and 25 (to the flash memory card slot 23 ofFIG. 1) that are connected to output contacts on the chip 43. Interfacecircuits 65 communicate between the lines 17, 45 and 55 (see FIG. 1) andthe processor 57 and the memory management unit 61.

Circuits 67 of FIG. 2, also connected with the processor 57 and memorymanagement unit 61, are optionally included to perform at least some ofthe repetitive specialized calculations necessary to implement theprocesses described herein, such as to estimate motion of the image fromdata of successive image frames. This is usually more efficient thanemploying the processor 57 to make the calculations under control of thefirmware but such calculations could alternatively be made by theprocessor.

Calculating Exposure Parameters

FIG. 3 is a flowchart that illustrates an example of a processimplemented within a camera such as illustrated in FIGS. 1 and 2 tocalculate exposure parameters for use in acquiring data of an image. Anyartificial illumination of the scene whose images are being captured isnot controlled in the process illustrated in FIG. 3.

Once the camera is turned on by the user, it repetitively acquires dataof images, as indicated by a step 71, at many frames per second, whichcan be as high as 30 or more. In the usual camera, these pre-captureimages are displayed in sequence on the camera's LCD display with areduced resolution, as a preview of an image that the camera wouldcapture when its shutter button is pushed but they need not bedisplayed. Two other calculation functions 73 and 75 are performed eachtime data of a new pre-capture image are acquired. This processing iscontinuous while the camera is being used. When it is detected that thecamera user has depressed the shutter button to take a picture, asindicated by a step 77, the quantities and parameters calculated insteps 73 and 75 are ready for use in setting up the camera up to quicklytake the picture. Alternatively, however, the calculations 73 and 75could be made after the step 77 has detected depression of the shutterbutton.

In the step 73, data of N number of pre-capture images are used tocalculate motion quantities for use in setting the exposure parameters,where N equals two or more, and can be five or more. As explained indetail below, any change in motion of the scene image relative to thecamera's photosensor is detected and quantified by looking at changes insuccessive pre-capture images, both globally (movement of the entireimage) and locally (local movement within the image). Vectors of motion,velocity and acceleration are preferably calculated from data of Npre-capture images, thereby allowing a prediction to be made of thefuture location of the scene image, or a portion of it, on thephotosensor.

In the step 75, exposure parameters are calculated by existingtechniques, without regard to any image motion, in order to maintain theaverage luminescence across the image within a predefined range. Theaverage luminescence can be measured from a pre-capture image. The timeduration of the exposure and one or more other exposure parameters arecalculated in this step. The other exposure parameters typically includethe size of the aperture opening and gain. However, although theseparameters are used directly to set current cameras to take a picture,they are treated in the camera operation shown in FIG. 3 as preliminary,subject to modification by the results of the motion calculations 73.

Once depression of the shutter button is detected by the step 77, thepicture could be taken as soon thereafter as possible. However, it ispreferred to first look at the motion quantities calculated in the step73. Taking of the picture may then be postponed for a time until anymotion of the image is expected to be minimal, in order to minimize anymotion blur in the resulting image. Therefore, in a step 79, the optimuminstant to take the picture is estimated from the motion quantitiescalculated in step 73. This estimate is made by extrapolating the motionquantities calculated from the pre-capture images in the step 73, andthen identifying either zero or minimal motion within a set period. Itis at that instant that the picture is scheduled to be taken. If,however, a zero or minimal motion point cannot be detected with highprecision, due to the complexity of the motion, or if the user haschosen to turn off the delayed capturing option, or if the motionquantities show that there is little or no motion of the image, then thetime for taking the picture is not postponed and capture of the image isexecuted right away.

A next step 81 determines whether the exposure parameters automaticallycalculated in the step 75 are such that the motion quantities will notcause them to be altered. For example, if the exposure duration (shutterspeed) is set by the step 75 to be below a certain threshold, then nofurther decrease of the exposure time to reduce motion blur should bedone. And if the aperture and gain are also set by the step 75 to besmaller than corresponding thresholds, then it is not necessary toconsider whether motion in the image is small enough to allow theshutter speed to be increased in order to lower them to improve depth offield or reduce noise. In such a case, which occurs for example, in avery brightly illuminated scene, the processing proceeds to a step 83where the picture is taken with the exposure parameters set by the step75. The motion quantities calculated in the step 73 are not used or evenreferenced. Nor is the calculation of step 79 of the time to take thepicture necessary; the picture can be taken right away.

However, in most situations the scene is not so brightly illuminated.Therefore, when the preliminary parameters calculated by the step 75 arenot within optimum ranges, they are adjusted by a step 85 in order tooptimize them for the amount of motion that was calculated by the step73. Generally, if that motion is high, the exposure time is reduced,with a corresponding increase in the size of the aperture and/orincrease in the gain in order to maintain the same average image signalluminescence. This reduces motion blur, but the depth of field generallywill decrease and/or the noise of the image may increase. But thistradeoff will almost always be preferred to acquiring an image withmotion blur.

On the other hand, if the calculated motion is low or zero, the exposuretime may be increased, with the benefit that the size of the apertureand/or the gain may be decreased. This provides an image with a greaterdepth of field, less optical blur and less noise. Without having thecalculated motion quantities, it would be risky to adjust thepreliminary parameters calculated by the step 75 in this way since itcould result in increased motion blur in the image when motion ispresent.

FIG. 4 conceptually shows a single image with its pixels grouped intoblocks of multiple pixels each, such as blocks 87 (represented by the i,j coordinates 3,6) and 89 (2,3). Motions of the scene being photographedrelative to the camera image frame are indicated. An example image isillustrated to have a global motion vector M_(G) indicated by arrows 91in each of the blocks of pixels. This motion would result from camerashake, back-and-forth in a horizontal direction. Of course, other cameramotion would be illustrated by different patterns. If the motion isup-and-down, for example, the global motion arrows would be shownvertically. If the camera motion follows a circular or ellipticalpattern, two other possibilities, the motion would be shown by a circleor ellipse, respectively.

The magnitude and direction of global motion is calculated from data ofN pre-capture images, preferably by the circuits 63 (FIG. 2), bydetecting and quantifying overall movement between the pre-captureimages. An example of a specific technique for calculating global motionis given in U.S. patent application Ser. No. 10/897,186, filed by Pintoet al. on Jul. 21, 2004. Alternatively, a mechanical motion sensor canbe included in the camera for the purpose of providing a signal of theglobal motion but is not preferred.

In the example of FIG. 4, a portion of the image is shown to haveadditional local motion vectors M_(L), in this case for four of theblocks, which are independent of any camera shake or other globalmotion. This represents motion of that small part of the scene beingphotographed relative to the rest of the scene and to the person holdingthe camera. The resulting motion within the image is in the direction ofthe arrows and with a relative velocity represented by the length of thearrows. Such motion can be from the movement of a person in the scene,vehicle motion, the action of wind on a tree, or from numerous othermovements in scenes that are photographed. Algorithms for thecalculation of motion within an image of between a sequence of imagesare known. An example is described in the above-identified U.S. patentapplication Ser. No. 10/897,186. Motion vectors can be calculated in amanner that is similar to the calculation of motion vectors used byknown video compression algorithms, examples being those of the MovingPicture Experts Group, the most recent being MPEG-4.

By one motion calculation technique, vectors of motion, velocity andacceleration are calculated for each of the blocks of pixels of theimage. These quantities give the motion of each block and allow itsfuture location, speed and direction to be estimated. If a large objectmoves across the scene, for instance, then the blocks representing theobject have motion vectors that point in the direction of the movement.If the image motion is due to camera shake only, the block motionvectors of all or most of a scene generally point in the same direction.The local motion vectors M_(L) of this description are these individualblock motion vectors after the global motion vector M_(G) has beensubtracted, so the vectors M_(L) provide an indication of only localmotion within the image of the scene. The vectors M_(L) and M_(G) are tothat extent independent of each other.

Curves of FIGS. 5A-5D provide an example of absolute values of local andglobal velocity vectors as a function of time, and combinations of them,in order to further describe the calculations of steps 73 and 79 (FIG.3). FIG. 5A shows the global motion represented by the arrows 91 of FIG.4. In this example, a back-and-forth motion of a camera is represented,having a zero speed (absolute velocity) at one extreme of its motion, azero speed at the other end of its motion, and an increasing-decreasingspeed function in between. FIG. 5C shows an example of the magnitude oflocal motion vector 93 of the pixel block 89 of FIG. 4. For illustrativepurposes, this motion is shown to increase from zero to a maximum andthen decrease during the pre-capture images. FIG. 5B shows the absolutevalue of a total motion vector M_(T(2,3)) for only the pixel block 89.This is an arithmetic combination of the magnitudes of the curves ofFIGS. 5A and 5C.

FIG. 5D shows an example of the total motion quantity M_(T) for theentire image frame. The motion calculations result in one value of M_(T)for each pre-capture image frame, and this is not a vector. It is theprimary quantity used in the steps 79 and 85 (FIG. 3) to determine anexposure time and adjust the exposure parameters. Indeed, the quantitiesM_(T) for a number of successive pre-capture images are used when it isdesired to estimate a better time for the exposure. For these purposes,it is a combination of the global motion of FIG. 5A and a weightedaverage of the local motion quantities of the individual pixel blockswithin the image. An equation for calculating M_(T) of an image frame isgiven in FIG. 5D. The weight W of an individual pixel block (i,j) can bemade to depend on its location within the image frame or on its relativeluminance with respect to the rest of the image. The weight W may be afunction of the distance of the block from the center of the imageframe. Therefore, the total motion M_(T) for an image depends on thenumber of blocks having local motion, the magnitude of that local motionand the relative position of the blocks with motion within the image.Further, the global motion M_(G) may be multiplied by a constant k, asshown in the equation of FIG. 5D, to allow different weights to be givento the global velocity and the average of local velocities. If k is morethan one, the global motion is weighted more and if less than one thelocal motion carries the greater weight. The overall total motion curveof FIG. 5D is similar to the total motion curve of FIG. 5B for a singlepixel block, but lower in magnitude because the local motion of mostpixel blocks of the image frame of FIG. 4 that are included in theaverage is zero.

In the example of FIGS. 5A-5D, data for pre-capture images are beingacquired in the period before time t1. If the step 79 (FIG. 3) is beingimplemented, then the motion after acquiring the last pre-capture imageat time t1 is estimated from data of the pre-capture images, as showndashed in FIGS. 5A-5D. The motion detected from the pre-capture imagesis extrapolated into the future. A period t1-t3 is preferably defined inwhich the minimum motion is sought to be identified. The total motion(FIG. 5D) is, in this example, the quantity for which minimum motion issought, and that total motion is zero at time t2. So that at time t2,the effects of motion on the picture being taken are estimated to beminimized, so this instant is selected to capture the image. Of course,actual motion functions can be more complicated than those illustratedin FIGS. 5A-5D, in which case a minimum value of M_(T) is sought withinthe time period t1-t3.

As an alternative to making exposure adjustments based on the totalmotion of the scene relative to the camera image frame, the local motionof only a portion of the scene may be used. For example, the camera maybe provided with a fixed or user definable outline, such as a rectangle,that can be positioned to surround a portion of the image for whichmotion compensation is primarily desired. In the example of FIG. 4, theuser could surround image blocks M_(L(2,3)), M_(L(3,3)), M_(L(3,4)), andM_(L(2,4)) with such an outline. This portion of the image could be anobject that is moving relative to other portions of the scene, such as avehicle or a person. The processing then calculates a single localmotion quantity, such as an average of the vector magnitudes for theseblocks, and this quantity is then used to minimize blurring of such anobject within the scene. To accomplish this, the local motion quantityis used in place of the total motion to determine the time to capturethe image and/or to adjust the exposure parameters. The local motion ofthe outlined portion of the scene is thus taken into account whilemotion of other parts of the scene are not.

FIGS. 6A, 6B and 6C help to illustrate the automatic exposurecalculation 75 (FIG. 3) and the choice that is made in the step 81 basedupon these calculations. A digital camera, for example, often has onlyseveral discrete levels of aperture opening from which a selection ismade to take a picture. Aperture openings 95-98 are shown in FIG. 6A.For each of these levels, there is a gain function such as illustratedin FIG. 6B and an exposure time (duration) function such as illustratedin FIG. 6C. A sloping portion 101 of the exposure duration curve (FIG.6C) extends between the same luminescent levels as a flat portion 103 orthe gain curve (FIG. 6B). The automatic exposure (AE) calculation ofpreliminary exposure parameters is accomplished by choosing acombination of aperture, gain and duration that provides an averageoutput signal of the photosensor for an image that is within apredetermined range for a wide variety of illumination levels of thescene being photographed. The average luminescence of the image ismaintained within boundaries. These calculations, made without benefitof image motion information, balances the desire for a short exposuretime in case there is significant image motion against the desires of adeep field of view and low optical blur (small aperture opening) and lownoise (low gain). Some level of image motion is necessarily assumed inthe calculation of the parameters but no information of any particularimage motion is used. It is in the step 85, that these preliminaryparameters are adjusted for image motion if such an adjustment willlikely improve the quality of the image.

The step 81 (FIG. 3), in this example, initially determines whether thecalculated automatic exposure quantities are all below levels T₁, T₂ andT₃ of FIGS. 6A-6C. If so, as previously discussed, there is no need toconsider the motion calculations. This is because adjustment of theexposure parameters cannot significantly improve image quality. Sincethe exposure time is nearly as small as possible, any motion blur cannotbe significantly reduced. In addition, there is no prospect of improvingthe depth of field or noise in the image by increasing the exposure timesince a compensating decrease in the aperture opening and gain are notpossible; they are already about as low as the camera allows.

FIG. 7 illustrates an example of step 85 of FIG. 3 for adjusting thepreliminary parameters in response to the motion calculations of thestep 73. For simplicity, there are four different sets 105-108 ofadjustments, depending upon the absolute magnitude of the total motionMT at the expected time of exposure. For the highest level 105, theexposure time is decreased significantly and one-half the imageluminescence lost, but that is restored by increasing the gain and theother one-half by increasing the aperture opening. In the next level106, with lesser motion, the exposure time is reduced by a smalleramount and the lost image luminescence restored by increasing either thegain or the aperture. If there is little or no motion, the level 108,the exposure time may be increased and the extra luminescence is reducedby reducing the gain and the aperture opening, both with beneficialresults on the captured image. If there is some small amount of motion,the level 107, the exposure time is increased a smaller amount andeither the gain or the aperture opening is reduced to restore the imagesignal to about the original level of luminescence.

In the examples of gain adjustment given above, the gain level of theanalog signal is adjusted before digitizing the signal and this adjustedlevel is then used during capture of the image. In addition to this, orin place of it, the gain of an image may be adjusted in the digitaldomain after data of the image have been captured and digitized. Forexample, the digital gain adjustment can be performed after the datahave been captured in the camera's internal memory, as part of imageprocessing or enhancement stage, but before compressing the data andwriting it to a removable non-volatile memory. Although digital gainincrease usually results in a noisier image than analog gain increase,it may be convenient to control the digital gain as well. The amount ofdigital gain that is required may be determined during the process thatadjusts the exposure parameters in advance of image capture, as part ofcalculating the exposure time, aperture and perhaps analog gain, butthen applied to the digital data of the image after it has already beencaptured. Alternatively, or in addition, the gain level of the image maybe determined and adjusted as part of the post-processing or enhancementof the captured image data and applied thereafter in that stage.

The parameter adjustment example of FIG. 7 shows several motionthresholds between the sets 105-108 of adjustments. For any motion abovethe threshold between the sets 106 and 107, the parameters areindividually adjusted in a single direction, and when the motion isbelow that threshold, the parameters are adjusted in the oppositedirection. As a variation of this single threshold, two motionthresholds can be defined. When the motion is above the higher of thetwo thresholds, the parameters are individually adjusted in onedirection and individually adjusted in the opposite direction when belowthe lowest threshold. For motion values between the thresholds, noadjustment of the preliminary parameters would be made.

Control of Artificial Illumination

In the above-discussion, the exposure parameters are calculated andutilized to capture data of images of scenes without regard to whetherthe scenes are illuminated by artificial light. Those techniques applyprimarily to situations where the scenes are illuminated by ambientlight. Sources of ambient light include sunlight, daylight, generalinterior building lighting, outdoor street lamps, and the like. But whenan artificial light pulse is used to illuminate a scene, usually inaddition to some level of ambient lighting, parameters of the lightpulse may also be controlled by any camera jitter or motion found toexist within the scene. Such parameters include the intensity andduration of the flash light pulse and its liming. At least one of theseparameters is controlled to reduce or eliminate blur in the image due toimage motion.

The flow chart of FIG. 8 illustrates an embodiment of such flash lightcontrol. The process is similar to that shown in FIG. 3 for calculatingand using exposure parameters on the basis of image motion, butadditionally calculates and uses parameters of artificial flash lampillumination on the basis of image motion. Indeed, if there issufficient ambient light illuminating the scene, steps 91 and 93 of FIG.8 can be the same as respective steps 71 and 73 of FIG. 3, providingdata of motion from data of two or more preview images of the scene.However, if insufficient ambient light is falling on the scene to allowthe accurate measurement of scene motion, the motion present in thescene may be measured in the step 93 while the scene is illuminated withtwo or more short flash light pulses, during respective two or moreexposures that acquire data of two or more preview images, as would beproduced by a standard gas discharge, for example a xenon, flash lamp.Or if more continuously illuminated by a highly controllableillumination source, such as one or more high brightness white, or othercolor, LEDs, a single long pulse may be used that extends over both ofthe preview image exposures. Indeed, the duration of the LED light pulsecan be further increased to extend over acquisition of data of both thepreview images and subsequently of the image of interest. Alternatively,separate pulses can be emitted from the LED during acquisition of one ormore of these images, in order to save power. In any of these cases,this “pre-flash” provides the necessary illumination to accuratelymeasure local motion of objects in the scene and/or global motion of theentire scene. In a step 95, the AE exposure parameters are calculated inthe same manner as described for the step 75 of FIG. 3, from pre-captureimages acquired when the scene is illuminated with ambient light,combined with motion vector information obtained while the scene isilluminated by “pre-flash” light.

In the process of FIG. 8, the desirability of using flash light for thecapture of the final image is determined by a technique not shown.Typically, the use of flash light is in response to either the averageluminance of the scene, illuminated with ambient light, being so lowthat the duration, aperture and/or gain required for a good exposureexceeds what the camera can provide. Sometimes flash is chosen becausethe luminance of some selected local portion of the image, containing anobject of interest, is below a set level, as would be the case if backlighting on a scene causes foreground areas of the scene to be in deepshadow, and therefore too weakly illuminated to allow the capture of forexample, facial details of a wife or child. Indeed, the object ofinterest may be an object with local motion such as an individual movingacross the scene, an automobile racing within the scene, etc.

After the shutter is detected to have been pressed, in a step 97, theduration and intensity of the flash pulse desired to be emitted duringcapture of the image are calculated, in a step 98. The pulse duration isdetermined primarily by the image motion quantities calculated in thestep 93. The pulse duration is selected to be short enough so that anyblur caused by motion of any part of or the entire image across thephotodetector during the duration of the pulse will be zero or less thansome acceptable level. The intensity of the flash pulse then needs to beadjusted so that the scene receives enough light energy to operatewithin a set of exposure parameters that are possible for the particularcamera or other digital image acquisition device. The initial set ofexposure parameters calculated in the step 95 may be adjusted in a laterstep 105 to adjust for the effect of the calculated flash pulse.

After the flash pulse and intensity are determined, a next step 99determines the best time to initiate the pulse. This is done in the samemanner as the calculation 79 of FIG. 3. The flash is preferablyinitiated at a time when the image motion calculated in the step 93 isexpected to be zero or at least a minimum within a short time intervalafter the start time calculation being made.

In a step 101, it is determined whether the initial exposure parameterscalculated in the step 95 need to be changed after the flash lightpulse, with characteristics determined by the step 98, has been added.If not, data of the image are captured in a step 103 with these initialexposure parameters and a flash light pulse generated with the durationand intensity calculated in the step 98. But if a change in one or moreexposure parameters is required, this is done in a step 105 before theimage is captured in the step 103. One change that may be necessary isto adjust the duration of the exposure that was calculated in step 95,as artificial light is to be added to the scene, due to activation ofthe flash light pulse. The exposure duration would then be typicallydecreased, as the overall scene is to be more illuminated, hence theblur effect would be additionally reduced. Changes in the initiallycalculated aperture and sensor gain may also be necessary in the step105 to accommodate the increased luminance of the scene caused by theflash light pulse and/or any increase in the exposure duration. Forinstance, sensor gain may be decreased to reduce overall image noise, oralternatively increased to increase image brightness.

Any such exposure parameter adjustments are made in the step 105 withouttaking into account any of the image motion quantities calculated in thestep 93. Any image motion is compensated in the embodiment of FIG. 8 bycontrol of the flash light in order to reduce or eliminate blur in theresulting image that is captured.

In another embodiment illustrated by the flowchart of FIG. 9, however,each of the flash light and exposure parameters are calculated from themotion that is forecasted to occur during exposure. Initial steps 111and 113 are again essentially the same as the steps 71 and 73,respectively, of the embodiment of FIG. 3. But in a step 115, initialparameters of exposure and flash are calculated according to currentknown algorithms used in cameras, without regard to any motion in theimage.

Once it is detected that the camera user has actuated the shutterbutton, in a step 117 of FIG. 9, the histories of the motion vectorscalculated in the step 113 are used to predict a time of zero or minimummotion within an allowed time horizon. It is at this time that theconcurrent exposure and flash light pulse preferably occur. This isessentially the same as the step 79 of the embodiment of FIG. 3,determined in the manner illustrated in FIGS. 5A-5D.

A next step 119 determines whether the initial exposure and flash lightparameters calculated in the step 115 are optimal in view of imagemotion calculated in the step 113 and the time of initiation of exposureand flash determined by the step 119. If so, data of the image arecaptured in a step 123 with the set exposure and flash light pulseparameters calculated in the step 115 being used. However, if theinitially determined exposure and/or flash durations are so long withrespect to the amount of motion present that an unacceptable amount ofblurring will occur in the image, or if the aperture or sensor gain areabove acceptable thresholds, modifications are taken in a step 125 tothe exposure and/or flash light parameters calculated in the step 115.Data of the image are then captured in the step 123.

The flow chart of FIG. 10 illustrates a more detailed embodiment ofartificial illumination control. The process there shown is insertedwithin the flowchart of FIG. 3 in a convenient place, such as betweenthe steps 77 and 79. The combination controls parameters of both theexposure and a flash light pulse. If flash light is enabled by thisadded process, then the adjustment in the step 85 (FIG. 3) of theexposure parameters includes making adjustments for the parameters ofthis added illumination.

A first step 131 of the sub-routine of FIG. 10 determines whether theluminance of the scene is above a first preset threshold. This is a highvalue, detected when the exposure duration, aperture and sensor gaincalculated in the step 75 are all below predetermined thresholds. If so,no flash is activated and the exposure parameters are calculated withoutconsideration of any artificial illumination. Any motion in the image isnot taken into account since the exposure duration is already as shortas possible and flash illumination of an already brightly illuminatedscene will have little effect. If below such a threshold, however, theprocess then proceeds to a step 133.

In the step 133, it is determined whether the ambient illumination ofthe scene is above a second preset threshold that is below the firstpreset threshold. The second threshold is established to identify sceneswith ambient illumination of at least a medium level that is high enoughto usually enable image capture without artificial illumination. At thesame time, the second threshold is set so that scenes with ambientillumination below it usually results in one or more of the exposureparameters to be calculated outside of its operating range and as aresult requires artificial illumination of the scene in order to acquirea good image. Therefore, when the scene ambient illumination is greaterthan the second threshold, the processing proceeds to a step 135 thattakes image motion into account when determining whether to utilize aflash or not. When below the second threshold, however, the processproceeds to a step 137 wherein a flash will be used unless, as indicatedby the presence of an intermediate step 139, there is some reason not todo so. One reason not to utilize a flash in this low ambient lightsituation is the desire of the camera operator to create an image thatlooks natural. That is, it is desired that the image not exhibit a rapiddecrease in illumination in the depth direction of the scene beingphotographed because it can cause an image to be overly bright forobjects close to the camera and very dark for objects far away from thecamera.

In the step 135 of FIG. 10, it is determined from the calculations ofthe step 73 (FIG. 3) whether a relevant one or more quantities of motionof the image exceed a predetermined quantity. If so, this indicates thatthe image captured without flash will contain a significant motion blur,and the process proceeds to the step 137 to enable the flash. In thestep 137, the parameters of duration, strength and timing of a flashlight pulse are calculated in the same manner as described above for thestep 98 of FIG. 8, and the flash is enabled to operate with theseparameters. But if, in the step 135, it is determined that no quantityof image motion exceeds the predetermined amount, the flash is usuallynot used. In this case, there is enough ambient illumination of thescene that the exposure parameters may be set to eliminate orsatisfactorily reduce the amount of image blur that may result from thesmall amount of image motion. The step 137 is then bypassed since theflash is not to be used. But if there is some other reason to use aflash, as determined by an intermediate step 141, then the step 137 isincluded and the flash used.

One reason to use a flash when there is enough ambient illumination, andinclude the step 137, is the desire of the camera operator to create animage that exhibits a greater dynamic range, lower noise level and/orgreater depth of focus than can be obtained when the picture is capturedwith ambient lighting alone, even though adequate illumination isavailable for use of a relatively short exposure duration tosufficiently freeze the motion of the object of interest in the scenebeing photographed. This scenario is chosen especially if a highlycontrollable illumination source is employed, such as one or more highbrightness white LEDs. In this case, the illumination pulse length caneasily be made to exceed a shutter controlled exposure duration that isshort enough to adequately freeze the motion in the scene butsignificantly longer than the pulse length of a conventional gasdischarge flash light. Thus, the light of the image falling on thesensor is integrated over a longer period of time, allowing both ambientlighting and flash lighting to contribute to the quality of the capturedimage. By using a smaller aperture and lower gain level setting than canbe employed by using only ambient lighting, a motion artifact is reducedand the captured image is more natural looking with a greater depth offocus and lower noise.

If it is determined in the step 135 that the motion blur will be inexcess of a set amount, parameters for the flash are calculated in thestep 137 and the flash enabled for use to capture data of the image.These parameters are calculated on the basis of the motion quantitiescalculated in the step 73 in order to eliminate or substantially reducethe motion blur that would otherwise exist.

In summary, the combined processes of FIGS. 3 and 10 are effective inreducing the amount of blur in an image of a scene that is moving, intotal or partially, with respect to the camera photosensor, as well asproviding for other image improvements by dynamically responding tolighting and motion conditions of the scene.

CONCLUSION

Although the various aspects of the present invention have beendescribed with respect to exemplary embodiments thereof, it will beunderstood that the present invention is entitled to protection withinthe full scope of the appended claims.

It is claimed:
 1. A method, comprising: receiving a plurality ofpre-capture images from one or more photo-sensors; and employing one ormore circuit components to perform actions, including: using at leastsome of the pre-capture images to determine a magnitude of image motionand acceleration, including a local acceleration, of at least some ofthe pre-capture images; and determining a time to initiate capture of another image based on the determined magnitude of image motion and atleast local acceleration.
 2. The method of claim 1, wherein the imagemotion and acceleration are determined for each of a plurality of blocksof pixels of the pre-capture images.
 3. The method of claim 1, furthercomprising: determining at least one exposure parameter from at leastthe determined magnitude of image motion; and further employing the atleast one exposure parameter to capture the other image.
 4. The methodof claim 1, further comprising: determining at least one illuminationparameter of the scene, based in part on artificial lightning of thescene, and from at least the determined magnitude of image motion; andfurther employing the at least one illumination parameter to capture theother image.
 5. The method of claim 4, wherein calculating the at leastone illumination parameter further comprises calculating at least aduration of at least one light pulse emitted by at least one flash lamp.6. The method of claim 1, wherein the magnitude of image motion isfurther employed to set a magnitude of at least one of a duration,aperture, or gain of an imaging device for capturing the other image. 7.The method of claim 1, wherein the magnitude of image motion is furtheremployed to set a timing of a light pulse to reduce blur of the capturedother image due to motion.
 8. A device, comprising: memory for storingan image of a scene; and one or more circuit components configured toperform actions, including: receiving a plurality of pre-capture imagesfrom the memory; using at least some of the pre-capture images todetermine a magnitude of image motion and acceleration, including alocal acceleration, of at least some of the pre-capture images; anddetermining a time when to initiate capture of an other image based onthe determined magnitude of image motion and at least localacceleration.
 9. The device of claim 8, wherein the one or more circuitcomponents are configured to perform actions, further including:determining at least one exposure parameter from at least the determinedmagnitude of image motion; and further employing the at least oneexposure parameter to capture the other image.
 10. The device of claim8, wherein the one or more circuit components are configured to performactions, further including: determining at least one illuminationparameter of the scene, based in part on artificial lightning of thescene, from at least the determined magnitude of image motion; andfurther employing the at least one illumination parameter to capture theother image.
 11. The device of claim 8, wherein at least the magnitudeof motion is employed to further set at least one of a duration,intensity or timing of a light pulse emitted by at least one source ofartificial light during capturing the other image.
 12. The device ofclaim 8, wherein two or more of the pre-capture images are acquiredduring illumination of the scene by preview light emitted by at leastone source of artificial light.
 13. The device of claim 8, wherein thedetermined magnitude of image motion is dynamically calculated based ona last N number of pre-captured images, where N is greater than two,until a shutter press is detected.
 14. The device of claim 13, whereinat least one exposure parameter is dynamically calculated based on thedetermined magnitude of image motion from the last N number ofpre-captured images, until the shutter press is detected.
 15. A camera,comprising: an optical component for use in capturing images of a scene;and one or more electronic components arranged to perform actions,including: receiving a plurality of pre-capture images from the opticalcomponent; using at least some of the pre-capture images to determine amagnitude of image motion and acceleration, including a localacceleration, of at least some of the pre-capture images; anddetermining a time when to initiate capture of an other image based onthe determined magnitude of image motion and at least localacceleration.
 16. The camera of claim 15, wherein the one or moreelectronic components arranged to perform actions, including: employingthe determined magnitude of image motion and acceleration including alocal acceleration to set a magnitude of at least one of a duration,intensity, or timing of a light pulse emitted by at least one source ofartificial light while capturing of the other image.
 17. The camera ofclaim 15, wherein the one or more electronic components arranged toperform actions, including: determining at least one exposure parameterfrom at least the determined magnitude of image motion; and furtheremploying the at least one exposure parameter to capture the otherimage.
 18. The camera of claim 15, wherein the one or more electroniccomponents arranged to perform actions, including: determining at leastone illumination parameter of the scene, based in part on artificiallightning of the scene, from at least the determined magnitude of imagemotion; and further employing the at least one illumination parameter tocapture the other image.
 19. The camera of claim 18, wherein calculatingthe at least one illumination parameter further comprises calculating atleast a duration of at least one light pulse emitted by at least oneflash lamp.
 20. The camera of claim 15, wherein the magnitude of imagemotion is further employed to set a magnitude of at least one of aduration, aperture, or gain of an imaging device for capturing the otherimage.